Method of chemical mechanical polishing

ABSTRACT

A method of planarizing a substrate employs two separate chemical mechanical polishing (CMP) steps. In the first CMP step, the substrate is polished using a first CMP slurry solution and a polishing pad. A diluting solution is then applied to the polishing pad to remove slurry of the first CMP step. In the second CMP step, after applying the diluting solution to the polishing pad to remove the first slurry, second CMP slurry solution is applied to the polishing pad to facilitate additional planarization of the substrate. In a particular embodiment of this invention, the diluting solution comprises a buffer solution having a pH level corresponding to a pH level of one of the first or second CMP slurry solution. In accordance with another aspect of this embodiment, a plurality of different diluting solutions are applied to the polishing pad intermediate the respective first and second CMP steps.

BACKGROUND OF THE INVENTION

The present invention relates generally to planarization of a substrate;and more particularly relates to chemical mechanical polishing (CMP) ofa semiconductor substrate employing two separate chemical mechanicalslurry solutions.

During fabrication of certain semiconductor devices, a metal layer,e.g., tungsten or aluminum may be deposited upon an underlying patterneddielectric layer, e.g., phosphosilicate glass (PSG), borosilicate glass(BSG), borophosphosilicate glass (BPSG) or silicon dioxide (SiO₂), toform interconnects, for example, within a semiconductor. In forming theinterconnects, chemical mechanical polishing of the metal layer removesmetal material until reaching the dielectric. Ideally, the polishedsubstrate has a flat surface, leaving metal in voids of the patterneddielectric to serve as interconnect plugs. These interconnects shouldeach have a flat upper surface that is flush with an upper plane definedby the top surfaces of the patterned dielectric layer. When a subsequentmetal layer is deposited, the deposited metal electrically connects withends of the plugs. The interconnect plugs, therefore, provide electricalconnections between the upper metal to respective lower semiconductorregions therebelow.

Available CMP procedures for planarizing a metal layer relative to apatterned dielectric for the formation of an interconnect plug oftenresult in undesirable divits, surface unevenness, or salt residues.Assuming a known planarization procedure employing two separate CMPslurry solutions, it is theorized (pursuant this disclosure), that theaddition of a second CMP slurry solution to a polishing procedure whilefirst CMP slurry solution is still present, may alter a pH of thepolishing procedure. This change in pH level, in-turn, may effectformation of precipitates, causing the slurry solution to gel and/orprovide salt formations.

Furthermore, when injecting different slurry solutions onto a polishingpad at different times during polishing of a semiconductor substrate,the pH of the combined solutions is not precisely controlled; rather,the pH level is in a state of fluctuation as the new slurry solution isdispensed onto the pad and mixed with solutions already on the pad.Thus, the resulting CMP process rate and selectivity are not preciselyknown. For example, the slurries of certain known CMP processes forpolishing tungsten have been found to chemically attack the tungstenlayer and create undesirable voids within exposed tungsten plugs, orresult in the formation of vias during later process stages.Additionally, if there is a loss of oxide selectivity (for the abovedescribed example where the oxide layer serves as the patterneddielectric beneath the tungsten), the lack of oxide selectively mayresult in complete removal of certain oxide portions so as to expose anddamage underlying semiconductor devices beneath the oxidelayer--resulting in scrapped material.

SUMMARY OF THE INVENTION

The chemical etch rate of certain materials is strongly dependent on apH level of the associated slurry solution. Accordingly, the presentinvention provides new methods for polishing of a substrate, whichmethods provide greater control of the pH level during the planarizationprocedures.

During a polishing procedure, a second slurry solution is dispensed ontoa polishing pad following use of a first slurry solution, providing aslurry solution transition to alter characteristics of polishing of asemiconductor substrate. The second slurry solution may have a pH thatis different from the first solution. Since the polishing pad used forpolishing the substrate has a capacity to absorb slurry, a preciseswitch from one pH to another pH during the polishing of the substrateis not readily available. In accordance with one embodiment of thepresent invention, a diluting solution is dispensed onto the polishingpad as an intermediate step between the application of respective firstand second slurry solutions to the polishing pad. The diluting solutionassists neutralization of the polishing pad before the application ofthe second slurry solution.

In accordance with one aspect of this particular embodiment of thepresent invention, a substrate is polished using a first slurry solutionand a polishing pad. Thereafter, the first slurry solution issubstantially removed from the polishing pad using at least one dilutingsolution. After this step of applying diluting solution to the polishingpad to remove the first slurry solutions, the substrate is furtherpolished using a second slurry solution.

In a preferred aspect of this embodiment of the present invention, thefirst slurry solution is removed from the polishing pad using (as thediluting solution) a first buffer solution having a pH to the same sideof 7 as that of the first slurry solution. Following use of the firstbuffer solution, a solvent is applied to the polishing pad forneutralizing a pH level. Preferably, the buffer solution and/or solventare applied to the polishing pad during relative movement of thesubstrate against the polishing pad and during mechanical conditioningof the polishing pad.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood from reading the followingdescription of particular embodiments, with reference to the attacheddrawings as listed below, where:

FIG. 1 is a partial, cross sectional, simplified view representative ofa chemical mechanical polishing (CMP) machine for polishing a substrate;

FIG. 2 is a partial, simplified block diagram view representative of theCMP polishing apparatus of FIG. 1 for polishing a substrate;

FIG. 3 is a simplified flow chart representative of a CMP procedure ofthe present invention; and

FIGS. 4-6 are cross sectional views of an exemplary substrate forillustrating various stages of a CMP procedure of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to FIGS. 1 and 2, a chemical mechanical polishing (CMP)apparatus includes a polishing table 18 coupled to a table shaft 31 forholding and rotating a polishing pad 16 on an upper surface of thepolishing table 18. Wafer carrier 10 has a polishing head 27 coupled toan associated shaft 33. Polishing head 27 has a lower surface forseating substrate 12 in face-to-face relationship with a polishingsurface of polishing pad 16. Shaft 33 of wafer carrier 10 can be rotatedor moved using known means for moving a surface of substrate 12 relativepolishing pad 16. In addition, a downward force 11 is typically appliedto wafer carrier 10 for pressing the surface of substrate 12 against thepolishing surface of polishing pad 16.

Although not shown specifically, polishing head 27 of wafer carrier 10preferably has a slight recess for receiving substrate 12 therein.During polishing, fluids provide an adhesive force between substrate 12and polishing head 27 for keeping substrate 12 adhered to polishing head27 by way of the surface-tension effects therebetween. Although, thepolishing head, in a preferred embodiment, has a recess for seatingsubstrate 12; polishing head 27 alternatively employs other knownsubstrate adhesive provisions. By way of example, polishing head maycomprise an intermediate poromeric material consisting of a fiberreinforced polyurethane foam as described in U.S. Pat. No. 3,841,031,issued Oct. 15, 1974, to Robert J. Walsh, entitled "Process forPolishing Thin Elements", the disclosure of which is hereby incorporatedby reference in its entirety.

Preferably, wafer carrier 10 can be moved radially in or out relativethe center of polishing table 18. Additionally, head shaft 33 is capableof being rotated at the same time that table shaft 31 of the polishingtable 18 is rotated, as shown by the respective arrows of FIG. 2 of thepresent application, and includes provisions to apply force to asubstrate for gently holding the substrate under pressure against apolishing head during rotation and/or oscillation of head shaft 33 androtation (or oscillation) of polishing table 18.

Solution delivery tube or pipe 23 (with reference to FIGS. 1 and 2) hasan ejection outlet, or nozzle, positioned over the polishing surface ofpolishing pad 16 for enabling delivery of various solutions to thesurface of polishing pad 16. FIG. 1 shows only one solution deliverytube 23 over the polishing table 18; however, it will be understood thata plurality of solution delivery tubes 23 (as shown in FIG. 2) could beprovided for delivering one or a plurity of associated solutions to thepolishing surface of polishing pad 16. Such a multiple solution deliverysystem is described in U.S. Pat. No. 5,540,810, issued Jul. 30, 1996, toGurtej Sandhu et al, entitled "IC Chemical Mechanical PlanarizationProcess Incorporating Two Slurry Compositions for Faster MaterialRemoval Times", the disclosure of which is hereby incorporated byreference in its entirety.

With reference to FIG. 2, solution delivery tube 23A has one enddisposed over the polishing pad 16 for dispensing a diluting solution asreceived from a reservoir 27. Similarly, solution delivery tube 23B hasone end disposed over the polishing pad 16 proximate the outlet ofdelivery tube 23A to deliver, for example, a slurry solution from anassociated reservoir 25. Not shown, although implied, are appropriatepumps and valve regulators for controlling flows of slurry solution anddiluting solution through respective solution delivery tubes 23 onto thepolishing surface of polishing pad 16. Additionally, it will beunderstood that the solution supplied to respective delivery tubes 23may be altered in known fashion using a control valve in selectivecommunication between separate supply reservoirs of different solutions.Additionally, although not shown, solution delivery tube(s) 23, is (are)mounted to an appropriate control arm that provides variably controlledpositioning of the outlet(s) of tube(s) relative the polishing surfaceof polishing pad 16.

An additional optional element for the CMP polishing apparatus, as shownin phantom-lines in FIGS. 1 and 2, is mechanical conditioner unit 15.Face plate 19 of mechanical conditioner 15 has conditioner tips 21 on alower surface thereof for meeting the polishing surface of polishing pad16. During conditioning, conditioner tips 21 penetrate the polishing pad16 to a depth established in accordance with a height of the conditionertips 21, the height of the tips being established relative to a bottomhorizontal surface of face plate 19. The bottom horizontal surface offace plate 19 acts as a mechanical-stop, keeping the conditioner tips 21at a preferred penetration depth. During mechanical conditioning of thepolishing pad 16, polishing table 18 is rotated while conditioner tips21 of the conditioner 15 are held against the polishing surface ofpolishing pad 16. Additionally, shaft 17 of the mechanical conditioner15 is rotated, and moved radially relative polishing table 18 so as tofacilitate complete coverage and conditioning of polishing pad 16.

CMP machines are available from companies such as Strausbaugh orItec/Westech. Exemplary CMP polishing pads are available from companiessuch as Rodel, Dupont or Clarino. In one preferred embodiment andimplementation of the invention, the CMP polishing pad for performingthe process of the present invention is an IC-1000 Rodel polishing pad,configured in a pad stack arrangement (not shown) with an FR-4 underpadalso of Rodel. Although specific CMP machines, polishing pads, andsubstrate mounting techniques have been disclosed for carrying out CMPprocedures of the present invention, it is to be understood that themethods and techniques of the present invention may be carried outsimilarly using alternative CMP machines, polishing pads, substratemounting and/or mechanical conditioning tools.

During polishing of a surface of a substrate 12, the surface ofsubstrate 12 is held against a polishing surface of polishing pad 16 andmoved relative thereto while chemical mechanical polishing (CMP) slurrymixtures are dispensed and applied to the surface of polishing pad 16for facilitating planarization of substrate 12. During the polishingprocedure, the rotational movement of polishing pad 16 will cause slurrysolution to flow radially outward. Some of the slurry solution will flowoff polishing pad 16 due to the centrifugal forces of the rotation.Accordingly, in order to keep an adequate amount of slurry on thepolishing pad during polishing, solution is typically supplied topolishing pad 16 continually during the CMP operation.

As used hereinafter, diluting solution refers to a diluent used to washaway material from the polishing pad, i.e., a liquid applied to thepolishing pad for cleansing the polishing surface. The diluting solutionin one exemplary embodiment comprises a buffer solution, oralternatively, simply a solvent. A buffer solution refers to a knownsolution comprising both a weak acid and weak base and having theability to absorb small additions of acids and bases without giving riseto a significant change in the pH of the solution. A known solventgenerally refers to a liquid capable of dissolving or dispersing othersubstances, typically the substance of greatest proportion in a solutionin is deemed the solvent. However, in solutions that contain water,water is typically deemed the solvent.

In certain polishing procedures, it is desirable to employ a firstslurry solution during a preliminary polishing step (for removing, forexample, a first layer of material from the substrate 12) followed by asubsequent polishing step that employs a different slurry solution.During the second polishing procedure, for example, a subsequent amountof the material is removed from the substrate.

For purposes of illustration, with reference to FIGS. 4-6, a preliminaryportion 28 of material 20 (e.g. tungsten) is removed from substrate 12by way of a first polishing procedure. Thereafter, a subsequent portion26 of material 20 is removed using a second slurry solution untilachieving a desired planar arrangement of material 20 relative secondarymaterial 22, for example, tungsten relative a dielectric. During thefirst polishing step for the removal of the first portion 28 of material20, it may be desirable to employ a first chemical-mechanical polishing(CMP) slurry mixture for providing an efficient first removal rate forremoval of material 20. Thereafter, the remaining polishingplanarization step could employ a different slurry solution thatprovides a reduced etching characteristic for etching of material 20relative material 22. In such circumstances, the first CMP polishingstep may employ an acidic CMP slurry solution while the subsequentpolishing procedure may employ a basic CMP slurry solution. Whentransitioning between the different slurry mixtures, the subsequentslurry solution has typically been dispensed and applied to thepolishing surface of polishing pad 16 with residual remnants of thefirst slurry solution still present thereon. Accordingly, when theacidic solution, of the first polishing step, for example, meets a basicsolution of, for example, the second polishing step, it is theorized(pursuant this disclosure) that unwanted precipitates result. Suchprecipitates, e.g., a salt, can have an adverse impact upon the desiredpolishing of substrate 12. Accordingly, the present invention proposesan intermediate step of applying a diluting solution to a polishingsurface of a polishing pad intermediate the two separate polishing stepsof a multiple step polishing procedure. With reference to FIG. 3, thediluting solution is applied (step 44) to the polishing pad intermediatea transition from a first slurry solution to a second slurry solution.

The simplified flow chart of FIG. 3 outlines a chemical-mechanicalpolishing procedure of the present invention, which is described hereinwith reference to the exemplary substrate depicted in FIGS. 4-5. Withreference to FIG. 4, substrate 12 has been previously processed todefine first 22 and second 20 layers of material over a base substrate24. In the exemplary embodiment, base structure 24 comprises a siliconwafer. In alternative embodiments, base substrate 24 comprises othermaterials such as gallium arsenide, aluminum oxide, glass, ceramic, orother similar substrate material. In addition, although not shown, itwill be understood that base substrate 24 may be representative of apreviously processed substrate, upon which layers 22 and 20 are providedthereover. In one preferred embodiment of the present invention,materials 22 and 20 comprise a dielectric material and a metalrespectively. More particularly, dielectric 22 is a silicon basedinsulator such as silicon dioxide, or alternatively, phosphosilicateglass (PSG), borophosphosilicate glass (BSPG) or silicon nitride; andmetal 20 is tungsten, or alternatively, aluminum, titanium, or titaniumnitride. Alternatively, substrate 12 constitutes a base substrate alone(e.g., silicon, gallium arsenic, aluminum oxide, glass, ceramic) that isto be processed by the procedure of the present invention, after whichadditional materials will be layered thereover.

In a preliminary step, substrate 12 is secured to the polishing head 27of wafer carrier 10. In step 40, the exposed surface 31 of substrate 12(facing away from polishing head 27) is positioned for meeting thepolishing surface of polishing pad 16.

In step 42, a first CMP polishing solution is applied to the surface ofpolishing pad 16 while an appropriate force and respective rotationalmotions are applied to wafer carrier 10 and polishing table 18 tofacilitate planarization of surface 35 of substrate 12. The CMPpolishing of step 42, using the first CMP slurry solution, continuesuntil a majority 28 of layer 20 (e.g. tungsten) is removed fromsubstrate 12, as shown in FIG. 5. In a preferred embodiment of thepresent invention, the first CMP slurry mixture is an acidic pH (pHgreater than 7) slurry with alumina particles and provides efficientremoval of tungsten. Such CMP slurry solutions are available from Rodel,Inc, under the trademarks of MSW-1000 or MSW-2000.

After removing the first portion 28 of substrate 12 via the first CMPpolishing step 42, a diluting solution is applied to the polishingsurface of polishing pad 16 for clearing residual slurry (of the firstCMP step) from the polishing surface of polishing pad 16. In a preferredembodiment of the present invention, pad conditioner 15 scrubs thepolishing surface of polishing pad 16 while the diluting solution isdispensed onto the polishing pad 16. In accordance with one aspect ofthis preferred embodiment, the rotation of wafer carrier 10 andpolishing table 18 continue during the cleaning step, enabling removalof residual slurry from substrate 12 and polishing head 27 at the sametime. In alternative embodiments of the present invention, wafer carrier10 lifts substrate 12 from the polishing pad during the pad cleaningprocedure; and/or pad conditioner 15 is not used at all, during the timethat the diluting solution is dispensed upon the polishing pad.

As the diluting solution is applied to polishing pad 16, it ispreferably applied, firstly, near the center of the polishing pad.Thereafter, outlet 25 of solution delivery tube 23 is moved radiallyoutward away from the center of the pad, in order to dispense dilutingsolution upon other circumferential regions of polishing pad 16. A knownmechanical arm is operative to control the position of the solutiondispensing tube 23 relative the polishing table so as to move outlet 25of the tube along the radial direction away from the center of thepolishing table during the polishing pad cleaning step 44. Additionally,and regardless of the movement of delivery tube 23, as diluting solutionis applied to the polishing surface of polishing pad 16, rotation ofpolishing table 18 provides rotational centrifugal forces to flowdiluting solution (as dispensed thereon) along the surface and radiallyoutward from the center of polishing pad 16 so as to carry-away residualslurry from polishing pad 16.

Preferably, the diluting solution is dispensed from delivery tube 23 byway of a nozzle with sufficient velocity to agitate and loosen slurrymaterials on the polishing surface when the diluting solution strikesthe surface of the polishing pad. This fluid scrubbing action assistscleansing of polishing pad 16.

In one embodiment of the present invention, the diluting solutioncomprises a buffer solution having a pH level the same side of 7 as thatof the first CMP slurry mixture. In other words, if the CMP slurrysolution has an acidic pH level, the diluting solution used is a buffersolution of acidic pH; likewise, if the CMP slurry solution has a basicpH level, the diluting solution used is a buffer solution of basic pH.More preferably, the buffer solution has a pH level within two of thatof the first CMP slurry solution and prevents precipitates from formingon the polishing pad when the buffer solution mixes with the residualCMP slurry (e.g., of the first CMP procedure).

An exemplary basic buffer solution to be used in connection with a basicslurry, comprises 1-5 weight percent ammonium hydroxide and 0.5-2 weightpercent ammonium acetate in water providing a pH of about 8-10 pH.

In one embodiment and implementation of the present invention, the aboveexemplary buffer solution is used as a diluting solution to cleanse apolishing pad of previous SC-20 (KOH buffered) slurry, or ILD-1300(ammonium hydroxide buffered) slurry.

An exemplary acidic buffer solution to be used in connection with anacidic slurry, comprises about 20 parts by volume of ammonium fluoridesolution (80 weight percent in water) and 1 part hydrofluoric acid (49weight percent in water) providing a pH of about 4-5.

In another embodiment and implementation of the present inventions, theabove exemplary buffer solution is used as a diluting solution tocleanse a polishing pad of previous acidic pH slurry, e.g., MSW-1000 orMSW-2000.

Buffer solution, as the diluting solution, is applied to the polishingpad at a rate and duration to sufficiently clean the pad of first CMPsolution. In an exemplary procedure of this embodiment, polishing pad 16has a diameter of about 20-100 inches and a rotational speed of about10-70 rpm, and preferably receives buffer solution for a duration in therange of 5 to 120 seconds, and most preferably in the range, from 20 to30 seconds. The rate at which the buffer solution is applied to thepolishing pad, in this preferred embodiment, is in the range of 50milliliters to 1 liter per minute, or more preferably 100 to 300milliliters per minute. In a specific exemplary embodiment of thepresent invention, the buffer solution is dispensed at a rate of 200milliliters per minute. Of course, the amount of time that the buffersolution is applied to the polishing pad can be adjusted in accordancewith the size of the polishing pad, the amount of solution dispensed perunit time, the rotational speed of the polishing pad and cleanlinessdesired.

After cleaning the polishing surface of polishing pad 16 (per step 44),additional polishing of the substrate is provided in step 46 using asecond CMP slurry solution. In the exemplary embodiment of the presentinvention, remaining portion 26 of substrate 12 is removed using asecond CMP slurry solution having basic pH. Preferably, the second CMPslurry solution comprises either a potassium hydroxide or ammoniumhydroxide buffer based slurry with silica suspended therein forassisting oxide removal. Such slurry solutions are available from Rodel,Inc.--i.e., tradename SC-20 for a silica based potassium hydroxidebuffered slurry, or tradename ILD-1300 for a silica based ammoniumhydroxide buffered slurry. By sufficiently removing first slurrysolution from polishing pad 16 (e.g., using the associated dilutingsolution) before applying the second CMP slurry, precipitation ofunwanted particulate is minimized.

In one particular embodiment of the present invention, a single buffersolution (serving as the diluting solution) is dispensed over polishingpad 16 during cleaning step 44. Such a procedure can be used when thefirst CMP slurry mixture of step 42 and the second CMP slurry mixture ofstep 46 have comparable chemistries, e.g., both acidic or both basic or,alternatively, with pH levels within two of each other. In such case,the buffer solution serves to re-establish the pad's pH condition, topurge the pad of slurry accumulation or build-up, and to assistconditioning of the polishing pad.

On the other hand, if the pH level of the first slurry solution differssubstantially from the pH level of the second slurry solution, forexample, one is acidic and the other basic or, alternatively, the pHlevels differ from each other by more than two, then undesirableprecipitates could be formed if the two different solutions are combinedon the polishing pad, as might occur during a transition from the firstslurry to second slurry solution. Therefore, in accordance with onepreferred embodiment of the present invention, the polishing surface ofpolishing pad 16 is first neutralized before dispensing the second CMPslurry solution onto the polishing pad.

In accordance with this one embodiment of the present invention,assuming first and second CMP slurry solutions of substantiallydifferent pH chemistries, two separate diluting solutions are applied,at different time intervals, to the polishing surface of the polishingpad, intermediate the application of the respective first and second CMPslurry solutions. After polishing substrate 12 using the first CMPslurry solution of, for example, acidic pH (i.e. after completing step42), a buffer solution of (acidic) pH is applied to the polishingsurface of the polishing pad 16. The buffer solution serves as a firstdiluting solution for washing away particulate and residual material ofthe first CMP procedure. Thereafter, a second diluting solution isapplied to the polishing surface of polishing pad 16 for purging thepolishing pad 16 of the first diluting solution and for neutralizing theassociated pH. Preferably, the second diluting solution comprises asolvent, such as, for example deionized water. Alternatively, thesolvent comprises other suitable pH neutral solutions, such as, forexample, acetone or alcohol. Again, as similarly described hereinbefore,preferably, the pH neutralization solution or solvent is dispensed byway of a nozzle onto the polishing pad 16 with sufficient velocity so asto agitate and loosen particles and liquids as it impinges the surfaceand assist cleansing of previous diluting solution and/or slurry off ofthe polishing pad. Pad conditioner 15 and wafer carrier 10 each may ormay not be operative for conditioning polishing pad 16 and polishingsubstrate 12 respectively during the application of the second dilutingsolution. Once polishing pad 16 has been neutralized by the appropriateneutralization solution, the second CMP slurry mixture is dispensed ontopolishing pad 16 with reduced concern of undesirable precipitates orsalt formation.

In accordance with an additional, alternative aspect of this embodimentof the present invention, step 44 further comprises an additional stepof applying a third diluting solution to polishing pad 16 following theprevious applications of first and second diluting solutions. The thirddiluting solution is provided a pH level that is comparable with thesecond CMP slurry mixture. In certain procedures, residual dilutingsolution on polishing pad 16 may result in undesirable precipitation ofmaterials when the second CMP slurry mixture is combined therewith.Accordingly, this alternative procedure preconditions polishing pad 16with a solution having a pH level comparable with the pH of the secondCMP slurry mixture.

In other words, if the second CMP slurry solution is acidic, then thethird diluting solution is a buffer solution of acidic pH; if the secondCMP slurry solution is basic then the third diluting solution is abuffer solution of basic pH. Accordingly, the third diluting solutioncomprises a buffer solution with a pH level the same side of seven asthat of the second CMP slurry mixture, and more preferably, within twoof the pH of the second CMP slurry mixture. This buffer solution isapplied to polishing pad 16 for a duration sufficient to purge thepolishing surface of previous solutions. Again, wafer carrier 10 and padconditioner 15 may or may not be operable (but preferably, they are bothoperative) during the application of this third solution to polishingpad 16. After polishing pad 16 has been preconditioned with the thirddiluting solution, the second CMP slurry solution is applied to thepolishing pad 16 to provide additional chemical mechanical polishing ofsubstrate 12.

Thus, according to the polishing procedures of the present invention, asubstrate is polished using two different slurry solutions whileavoiding undesirable precipitation and/or salt formations.

In the exemplary embodiments of the present invention described above,the first CMP slurry solution was described as having an acidic pH whilethe second CMP slurry solution was characterized with a basic pH. Itwill be understood that the present invention similarly encompassesother CMP slurry sequences of different pH levels. Such alternativeslurry sequences would employ respective buffer solutions of similar pHlevels corresponding thereto. For example, it may be desirable to firstetch an oxide layer over a metal layer, wherein the first CMP slurrysolution could have a basic pH and the second CMP slurry solution anacidic pH. When employing three separate diluting solutions intermediatethe slurry transition, the first diluting solution comprises a buffersolution having a basic pH level that corresponds to the pH level of thefirst CMP slurry solution; the second diluting solution comprises anintermediate pH level solution (e.g., a neutral solvent); and the thirddiluting solution comprises a buffer solution having an acidic pH levelthat corresponds to the acidic pH of the second CMP slurry solution.

Likewise, although the CMP polishing procedures of the exemplaryembodiments described above were described for planarizing a metal overa dielectric; it is understood that the scope of the present inventioncould similarly encompass planarization of one particular dielectricmaterial relative a second type of dielectric material. For example,doped glass could be planarized relative undoped glass, silicon oxiderelative silicon nitride, or gallium-arsenide relativealuminum-gallium-arsenide. Similarly, the CMP polishing procedure of thepresent invention encompasses polishing of one electrically conductivematerial relative a second electrically conductive material--forexample, aluminum relative tungsten, tungsten relative titanium nitride,or copper relative silicon. During such polishing operations, CMP slurrytransitions need not be limited to acid base pH transitions. For theseparticular alternative applications, it may be desirable to shift from,for example, a strong acidic to a less acidic CMP slurry mixture. Inaddition, a slurry transition may comprise a switch from a silica basedCMP slurry solution to an alumina based CMP slurry solution.

In each of the above embodiments, an intermediate diluting solution isdispensed onto the polishing pad, intermediate a slurry transition, soas to purge previous solutions off of the polishing pad. Thisintermediate step offers advantages such as providing better control ofpH levels on the polishing pad and reducing undesirable artifactsassociated with mixing of different CMP slurry solutions.

It should readily be understood that the embodiments described andillustrated herein are illustrative only, and are not to be consideredas limitations upon the scope of the present invention. Other variationsand modifications may be made in accordance with the spirit and scope ofthe present invention.

What is claimed is:
 1. A method of polishing a substrate, comprising thesteps of:polishing the substrate using a first slurry solution and apolishing pad; removing at least a portion of said first slurry solutionfrom said polishing pad using at least one diluting solution, said atleast one diluting solution comprising a buffer solution; and after saidremoving of said portion of the first slurry solution, further polishingthe substrate using a second slurry solution and said polishing pad. 2.A method of polishing a substrate, comprising the steps of:polishing thesubstrate using a first slurry solution and a polishing pad; applying atleast one diluting solution to said polishing pad during relativemovement of the substrate against said polishing pad and removing atleast a portion of said first slurry solution from said polishing padusing said at least one diluting solution; and after said removing ofsaid portion of the first slurry solution, further polishing thesubstrate using a second slurry solution and said polishing pad.
 3. Amethod according to claim 2, wherein the step of removing includesapplying a solvent to said polishing pad.
 4. A method according to claim2, further comprising a step of employing a mechanical conditioner tomechanically condition said polishing pad while applying said at leastone diluting solution to said polishing pad.
 5. A method according toclaim 2, wherein the step of removing comprises applying deionized waterto said polishing pad.
 6. A method according to claim 2, wherein saidsecond slurry solution has a pH level that is different from a pH levelof said first slurry solution.
 7. A method according to claim 6, whereinsaid step of removing comprises the steps of:dispensing a first diluentto said polishing pad; and after dispensing said first diluent, applyinga second diluent to said polishing pad.
 8. A method according to claim7, wherein said first diluent is a buffer solution dispensed with a pHthe same side of seven as that of said first slurry solution.
 9. Amethod according to claim 8, wherein said step of removing includes astep of mechanically conditioning said polishing pad.
 10. A methodaccording to claim 8, wherein said step of applying the second diluentis performed for a sufficient duration to substantially neutralizechemistry of solution at said polishing pad before applying said secondslurry solution thereto.
 11. A method according to claim 7, wherein oneof said first diluent and said second diluent comprises a buffersolution and the other of said first diluent and said second diluentcomprises a solvent.
 12. A method according to claim 11, wherein saidsolvent, comprises at least one of the group consisting essentially ofdeionized water, acetone, and alcohol.
 13. A method of polishing asubstrate, comprising the steps of:polishing the substrate using a firstslurry solution and a polishing pad; dispensing a buffer solution tosaid polishing pad during relative movement of the substrate againstsaid polishing pad and removing at least a portion of said first slurrysolution from said polishing pad, said buffer solution having a pH thesame side of seven as that of said first slurry solution; afterdispensing said buffer solution, applying a diluent to said polishingpad, said diluent different from said buffer solution; and after saidremoving of said portion of the first slurry solution, further polishingthe substrate using a second slurry solution and said polishing pad. 14.A method according to claim 13, wherein said diluent is applied duringrelative movement of the substrate against said polishing pad.
 15. Amethod of chemically-mechanically polishing a surface of a substrate,comprising the steps of:disposing the surface of said substrate againsta polishing surface of a polishing pad; supplying a firstchemical-mechanical slurry to the polishing pad and polishing thesurface of said substrate with the polishing pad; after removing aportion of material from said substrate by way of the polishing withsaid first chemical-mechanical slurry mixture, applying a first dilutingsolution to the polishing pad and cleansing the polishing pad of atleast a portion of said first chemical-mechanical slurry; dispensing asecond diluting solution onto the polishing pad and cleansing thepolishing pad of at least a portion of said first diluting solution,said second diluting solution different from said first dilutingsolution; and after said cleansing of said portion of the first dilutingsolution, supplying a second chemical-mechanical slurry to the polishingpad and further polishing said substrate.
 16. A method according toclaim 15, wherein said first chemical-mechanical slurry has a first pHlevel and said second chemical-mechanical slurry has a second pH leveldifferent from said first pH level.
 17. A method according to claim 16,wherein said first chemical-mechanical slurry has a basic pH and saidfirst diluting solution comprises a buffer solution of basic pH.
 18. Amethod according to claim 16, wherein said first chemical-mechanicalslurry has an acidic pH and said first diluting solution comprises abuffer solution of acidic pH.
 19. A method according to claim 15,wherein said step of applying said first diluting solution to thepolishing pad comprises dispensing said first diluting solution througha nozzle onto a polishing surface of the polishing pad to loosenelements thereon as said first diluting solution impacts the polishingpad.
 20. A method according to claim 15, wherein said secondchemical-mechanical slurry has a basic pH and said second dilutingsolution comprises a basic pH.
 21. A method according to claim 15,wherein said second chemical-mechanical slurry has an acidic pH and saidsecond diluting solution comprises an acidic pH.
 22. A method ofchemically-mechanically polishing a surface of a substrate, comprisingthe steps of:disposing the surface of said substrate against a polishingsurface of a polishing pad; supplying a first chemical-mechanical slurryto the polishing pad and polishing the surface of said substrate withthe polishing pad; after removing a portion of material from saidsubstrate by way of the polishing with said first chemical-mechanicalslurry mixture, applying a first diluting solution to the polishing padand cleansing the polishing pad of at least a portion of said firstchemical-mechanical slurry; dispensing a second diluting solution ontothe polishing pad and cleansing the polishing pad of at least a portionof said first diluting solution, said second diluting solution differentfrom said first diluting solution, and wherein one solution of saidfirst and said second diluting solutions is a buffer solution and theother solution of said first and said second diluting solutions is asolvent; and after said cleansing of said portion of the first dilutingsolution, supplying a second chemical-mechanical slurry to the polishingpad and further polishing said substrate.
 23. A method according toclaim 22, wherein said solvent is selected from the group consistingessentially of deionized water, acetone and alcohol.
 24. A method ofchemically-mechanically polishing a surface of a substrate, comprisingthe steps of:disposing the surface of said substrate against a polishingsurface of a polishing pad; supplying a first chemical-mechanical slurryto the polishing pad and polishing the surface of said substrate withthe polishing pad; after removing a portion of material from saidsubstrate by way of the polishing with said first chemical-mechanicalslurry mixture, applying a first diluting solution to the polishing padand cleansing the polishing pad of at least a portion of said firstchemical-mechanical slurry, said first diluting solution comprising abuffer solution; applying a pH neutral solution to the polishing padafter said step of applying the buffer solution; and after saidcleansing of the polishing pad of said first chemical-mechanical slurry,supplying a second chemical-mechanical slurry to the polishing pad andfurther polishing said substrate.
 25. A method according to claim 24,wherein said step of applying said pH neutral solution comprisesdispensing said pH neutral solution through a nozzle onto a polishingsurface of the polishing pad and agitating elements thereon as said pHneutral solution impacts the polishing pad.
 26. A method ofchemically-mechanically polishing a surface of a substrate, comprisingthe steps of:disposing the surface of said substrate against a polishingsurface of a polishing pad; supplying a first chemical-mechanical slurryof a first pH level to the polishing pad and polishing the surface ofsaid substrate with the polishing pad; after removing a portion ofmaterial from said substrate by way of the polishing with said firstchemical-mechanical slurry mixture, applying a buffer solution to thepolishing pad to remove at least a portion of said firstchemical-mechanical slurry from the polishing pad; and after applyingsaid buffer solution to the polishing pad, supplying a secondchemical-mechanical slurry of a second pH level to the polishing pad andfurther polishing said substrate, said second pH level different fromsaid first pH level; said buffer solution provided a pH level within twopH units of one of said first pH level and said second pH level.
 27. Amethod according to claim 26, wherein said pH neutral solution isselected from the group consisting essentially of deionized water,acetone, and alcohol.
 28. A method of chemically-mechanically polishinga surface of a substrate, comprising the steps of:disposing the surfaceof said substrate against a polishing surface of a polishing pad;supplying a first chemical-mechanical slurry of a first pH level to thepolishing pad and polishing the surface of said substrate with thepolishing pad; applying a first diluent to the polishing pad andcleansing the polishing pad of at least a portion of said firstchemical-mechanical slurry, said first diluent having a pH level withintwo pH units of said first pH level; applying a pH neutral solution tothe polishing pad and cleansing the polishing pad of at least a portionof said first diluent, said pH neutral solution selected from the groupconsisting essentially of deionized water, acetone, and alcohol; afterthe application of said pH neutral solution, applying a second diluentto the polishing pad, said second diluent has a pH level; and supplyinga second chemical-mechanical slurry to the polishing pad and furtherpolishing said substrate, said second chemical-mechanical slurry havinga pH level within two pH units of the pH level of said second diluent.29. A method according to claim 28, wherein a buffer solution isprovided as said second diluent.
 30. A method according to claim 26,further comprising a step of applying a pH neutral solution to thepolishing pad between said step of supplying first chemical-mechanicalslurry and said step of supplying second chemical-mechanical slurry. 31.A method of polishing a substrate, comprising the steps of:providing asubstrate having at least one layer of material to be polished;polishing the substrate using a first slurry solution and a polishingpad and removing a first portion of said one layer of material from thesubstrate; removing at least a portion of said first slurry solutionfrom the polishing pad using at least one diluting solution; and afterremoving first slurry solution from the polishing pad, further polishingthe substrate using a second slurry solution and the polishing pad andremoving a second portion of said one layer of material from thesubstrate.
 32. A method according to claim 31, wherein said materialcomprises a metal.
 33. A method according to claim 32, wherein saidmetal comprises at least one of the group consisting of tungsten,aluminum, titanium and titanium nitride.
 34. A method according to claim31, in which the step of removing said first slurry solution comprisesapplying said at least one diluting solution to the polishing pad duringrelative movement of the substrate against the polishing pad.
 35. Amethod according to claim 31, in which the step of removing said firstslurry solution employs a buffer solution as said at least one dilutingsolution.
 36. A method according to claim 31, in which said step ofremoving said first slurry solution comprises a step of applying asolvent to the polishing pad.
 37. A method according to claim 36,wherein said solvent comprises deionized water.
 38. A method accordingto claim 31, wherein said first diluent is dispensed to the polishingpad, and said step of removing said first slurry solution furthercomprises a step of applying a second diluent to the polishing pad afterdispensing said first diluent.
 39. A method according to claim 38, inwhich said first diluent is a buffer solution.
 40. A method according toclaim 39, wherein said first chemical-mechanical slurry has a first pHlevel and said buffer solution has a pH level within two of said firstpH level.
 41. A method according to claim 39, in which said buffersolution is dispensed onto the polishing pad during relative movement ofthe substrate against the polishing pad.
 42. A method according to claim41, in which said second diluent is applied to the polishing pad duringrelative movement of the substrate against the polishing pad.
 43. Amethod according to claim 38, wherein said step of removing said firstslurry solution further comprises mechanically conditioning thepolishing pad.
 44. A method according to claim 38, in which said step ofapplying the second diluent establishes a pH of about 7 on the polishingpad before the step of polishing the substrate with said secondchemical-mechanical slurry.
 45. A method according to claim 38, whereinone of said first diluent and said second diluent comprises a buffersolution, and the other of said diluents comprises a solvent.
 46. Amethod according to claim 45, wherein said solvent comprises at leastone of the group consisting of de-ionized water, acetone, and alcohol.47. A method according to claim 38, wherein said step of dispensing saidfirst diluting solution to the polishing pad comprises dispensing saidfirst diluting solution through a nozzle onto a polishing surface of thepolishing pad.
 48. A method of chemically-mechanically polishing asubstrate, comprising the steps of:providing a substrate having at leasta first layer of material; placing said substrate against a polishingsurface of a polishing pad; polishing a surface of said substrate usingthe polishing pad and a first chemical-mechanical slurry and removing afirst portion of said first layer of material; after removing the firstportion of said first layer of material, applying a first dilutingsolution to the polishing pad and cleansing the polishing pad of atleast a portion of said first chemical-mechanical slurry; and after saidcleansing, removing a second portion of said first layer of material bypolishing the surface of said substrate using the polishing pad and asecond chemical-mechanical slurry.
 49. A method according to claim 48,in which each of said polishing steps comprises removing electricallyconductive material for respective said first and said second portionsof said first layer of material.
 50. A method according to claim 49, inwhich each of said polishing steps comprises removing metal as saidelectrically conductive material.
 51. A method according to claim 49,wherein each of said polishing steps remove a metal of the groupconsisting essentially of tungsten, aluminum, titanium and titaniumnitride as said electrically conductive material.
 52. A method accordingto claim 48, further comprising a step of dispensing a second dilutingsolution to the polishing pad to cleanse the polishing pad of at least aportion of said first diluting solution.
 53. A method according to claim52, wherein said second chemical-mechanical slurry has a basic pH andsaid second diluting solution comprises a basic pH.
 54. A methodaccording to claim 52, wherein said second chemical-mechanical slurryhas an acidic pH and said second diluting solution comprises an acidicpH.
 55. A method according to claim 52, wherein one solution of saidfirst and said second diluting solutions is a buffer solution and theother a solvent.
 56. A method according to claim 55, wherein said firstdiluting solution comprises a buffer solution.
 57. A method according toclaim 56, wherein said first chemical-mechanical slurry has a first pHlevel and said buffer solution is provided a pH level within about 2 pHunits of said first pH level.
 58. A method according to claim 56, inwhich said step of dispensing the solvent neutralizes chemistry ofsolution on the polishing pad before the step of polishing the substratewith said second chemical-mechanical slurry.
 59. A method according toclaim 58, wherein said step of dispensing the solvent comprisesdispensing said solvent through a nozzle onto a polishing surface of thepolishing pad and agitating solution thereon as said solvent impacts thepolishing pad.
 60. A method according to claim 56, wherein said firstchemical-mechanical slurry has a basic pH and said buffer solution isprovided a basic pH.
 61. A method according to claim 56, wherein saidfirst chemical-mechanical slurry has an acidic pH and said buffersolution is provided an acidic pH.
 62. A method according to claim 56,further comprising a step of applying a third diluting solution to thepolishing pad after the application of said solvent, said secondchemical mechanical slurry having a second pH level and said thirddiluting solution having a pH level within two pH units of said secondpH level.
 63. A method according to claim 62, in which a second buffersolution is supplied as said third diluting solution.